Titanium, titanium based alloy, and nickel based alloy castings are used in large numbers in the aerospace industry. Many such castings are made by the well known investment casting process wherein an appropriate melt is cast into a preheated ceramic investment mold formed by the lost wax process. Although widely used, investment casting of complex shaped components of such reactive materials can be characterized by relatively high costs and low yields. Low casting yields are attributable to several factors including surface or surface-connected, void type defects and/or inadequate filling of certain mold cavity regions, especially thin mold cavity regions, and associated internal void, shrinkage and like defects.
Permanent mold casting has been employed in the past as a relative low cost casting technique to mass produce aluminum, copper, and iron based castings having complex, near net shape configurations. However, only fairly recently have attempts been made to produce titanium and titanium alloy castings using the permanent mold casting process. For example, the Mae et al U.S. Pat. No. 5,119,865 issued Jun. 9, 1992, discloses a copper alloy mold assembly for use in the permanent mold, centrifugal casting of titanium and titanium alloys.